CN113823722A

CN113823722A - Light emitting element and method for manufacturing the same

Info

Publication number: CN113823722A
Application number: CN202110648357.0A
Authority: CN
Inventors: 永田贤吾; 斋藤义树; 片冈惠太; 成田哲生; 近藤嘉代
Original assignee: Toyoda Gosei Co Ltd
Current assignee: Toyoda Gosei Co Ltd
Priority date: 2020-06-18
Filing date: 2021-06-10
Publication date: 2021-12-21

Abstract

The present invention provides a light emitting device having an n-type contact layer which is composed of AlGaN having Si as a dopant and in which the resistance is effectively reduced by the degeneracy of the Fermi level and the conduction band, and a method for manufacturing the same. As one embodiment of the present invention, a light-emitting element (1) is provided, which has a Fermi level and a conduction bandA degenerated n-type contact layer (12) composed of AlGaN, and a light-emitting layer (13) composed of AlGaN and laminated on the n-type contact layer (12), wherein the Al component of the n-type contact layer (12) is greater than that of the light-emitting layer (13) by 10% or more and 70% or less, and the n-type contact layer (12) contains a concentration at which the degeneration occurs and is 4.0 x 10¹⁹cm^‑3Si at the following concentrations.

Description

Light emitting element and method for manufacturing the same

Technical Field

The present invention relates to a light emitting element and a method for manufacturing the same.

Background

Conventionally, a technique of using a degenerately doped gallium nitride layer in a tunnel junction of a Light Emitting Diode (LED) is known (for example, see patent document 1). It is considered that the above-mentioned "degenerately doped" means that the fermi level overlaps with the conduction band by doping the dopant at a high concentration (degeneracy). Semiconductors whose fermi level is degenerate with the conduction band generally behave like metals with reduced resistance.

In addition, a light emitting device using p-type GaN as a material of a contact layer connecting a p-side electrode is known (see patent document 2). According to patent document 1, a p-type GaN layer or a p-type AlGaN layer can be used as a contact layer connecting the p-side electrode, but the p-type GaN layer is preferably used in order to improve the contact with the p-side electrode.

In addition, a light-emitting element using a tunnel junction is known (see patent document 3). In the light-emitting element described in patent document 1, a tunnel junction is formed between a p-type GaN layer and an n-type InGaN layer in a light-emitting layer, and a p-side electrode is connected to the n-type InGaN layer as a p-side contact layer. Therefore, both the p-side contact layer and the n-side contact layer can use an n-type semiconductor, whereby the n-side electrode and the p-side electrode can be formed of the same material.

Documents of the prior art

Patent document

Patent document 1: japanese patent No. 5726405

Patent document 2: japanese patent laid-open publication No. 2019-110195

Patent document 3: japanese patent No. 3786898

Disclosure of Invention

However, in n-type AlGaN in which Si is used as a dopant, if the Si concentration is increased, the resistance decreases as in a general semiconductor until a certain concentration, but if the concentration exceeds a certain concentration, the resistance starts to increase instead. This is considered to be because a recombination defect of a group III hole with Si occurs when the Si concentration exceeds a certain concentration. Therefore, even if the fermi level and the conduction band are degenerated by increasing the Si concentration in the conventional general method, the resistance cannot be effectively reduced due to the recombination defect of the group III hole and Si.

Accordingly, an object of the present invention is to provide a light emitting element having an n-type contact layer made of AlGaN in which the resistance is effectively reduced by degeneracy of the fermi level and the conduction band, and which includes Si as a dopant, and a method for manufacturing the same.

Further, since AlGaN having a low GaN or Al composition absorbs deep ultraviolet light, if a contact layer made of GaN or AlGaN having a low Al composition is used for the deep ultraviolet light emitting element, the light extraction efficiency is significantly reduced. Therefore, with the structure of the light-emitting element described in patent document 2, a deep ultraviolet light-emitting element having excellent light extraction efficiency cannot be obtained.

Therefore, another object of the present invention is to provide a light-emitting element which emits deep ultraviolet light, has low contact resistance between a p-side electrode and a contact layer, and suppresses absorption of light by the contact layer.

In addition, GaN or InGaN strongly absorbs light in the deep ultraviolet region due to the size of their band gap. Therefore, if the deep ultraviolet light emitting element is configured as the light emitting element described in patent document 3, the light emitted from the light emitting layer is strongly absorbed by the p-type GaN layer or the n-type InGaN layer, and the light extraction efficiency is lowered.

Therefore, another object of the present invention is to provide a deep ultraviolet light emitting element using a tunnel junction, which suppresses absorption of light by an n-type layer and a p-type layer forming the tunnel junction.

In order to achieve the above object, one embodiment of the present invention provides the following light-emitting elements [1] to [4] and the following methods for manufacturing the light-emitting elements [5] and [6 ].

[1]A light-emitting element is provided with: an n-type contact layer composed of AlGaN whose Fermi level is degenerated with a conduction band, and a light-emitting layer composed of AlGaN and laminated on the n-type contact layer, wherein the Al component of the n-type contact layer is larger than that of the light-emitting layer by 10% or more and 70% or less, and the n-type contact layer contains a concentration at which the degeneration occurs and is 4.0X 10¹⁹cm^-3Si at the following concentrations.

[2] The light-emitting element according to the above [1], wherein the Al component of the n-type contact layer is 50% or more.

[3]According to the above [1]Or [2]]The light-emitting element, wherein the concentration of Si contained in the n-type contact layer is 1.6X 10¹⁸cm^-3The above.

[4]According to the above [1]～[3]The light-emitting element according to any one of the above, wherein the n-type contact layer has a resistivity of 5 × 10^-2Omega cm or less.

[5]A method for manufacturing a light-emitting element includes the steps of: a step of forming an n-type contact layer made of AlGaN in which the Fermi level is degenerated with the conduction band by vapor deposition, and a step of forming a light-emitting layer made of AlGaN on the n-type contact layer; the Al component of the n-type contact layer is larger than that of the light-emitting layer by 10% or more and 70% or less, and the n-type contact layer has a concentration at which the degeneracy occurs and is 4.0X 10¹⁹cm^-3Si with a concentration below, wherein the V/III ratio of the raw material gas of the n-type contact layer in the step of forming the n-type contact layer is within the range of 1000 to 3200.

[6] The method of manufacturing a light-emitting element according to item [5], wherein a growth temperature of the n-type contact layer in the step of forming the n-type contact layer is 1150 ℃ or lower.

In order to achieve the above object, another embodiment of the present invention provides the following light-emitting elements [7] to [11 ].

[7] A light-emitting element is provided with: the light emitting device includes an n-type contact layer made of n-type AlGaN, a light emitting layer emitting deep ultraviolet light on the n-type contact layer, a current diffusion layer made of AlGaN containing two-dimensional hole gas on the light emitting layer, a p-type contact layer made of p-type GaN or p-type AlGaN having an Al component of 35% or less connected to a part of an upper surface of the current diffusion layer, an n-electrode connected to the n-type contact layer, and a p-electrode connected to the p-type contact layer.

[8] The light-emitting element according to the above [7], wherein the current diffusion layer includes: a first AlGaN layer composed of p-type AlGaN having an Al component in the range of 50% to 70%, and a second AlGaN layer composed of p-type or i-type AlGaN having an Al component in the range of 30% to 50% and provided directly on the first AlGaN layer,

the second AlGaN layer has the two-dimensional hole gas in the vicinity of an interface with the first AlGaN layer.

[9] The light-emitting element according to the above [7] or [8], wherein an area of a region of the upper surface of the current diffusion layer contacting the p-type contact layer is within a range of 40% to 80% of an area of an entire region of the upper surface.

[10] The light-emitting element according to any one of the above [7] to [9], wherein at least a part of a region of the upper surface of the current diffusion layer other than a region to which the p-type contact layer is connected is covered with a passivation film made of an insulating material.

[11] The light-emitting element according to any one of the above [7] to [10], wherein a light-reflecting layer is provided above a region of the upper surface of the current diffusion layer other than a region to which the p-type contact layer is connected.

In order to achieve the above object, another embodiment of the present invention provides the following light-emitting elements [12] to [16 ].

[12] A light-emitting element is provided with: a first n-type contact layer made of AlGaN, a light-emitting layer emitting deep ultraviolet light on the first n-type contact layer, a p-type layer made of AlGaN on the light-emitting layer, a second n-type contact layer made of AlGaN on the p-type layer, which forms a tunnel junction with the p-type layer and is degenerate in fermi level and conduction band, an n-electrode connected to the first n-type contact layer, and a p-electrode connected to the second n-type contact layer; the Al component of the second n-type contact layer is in the range of 40% to 70%.

[13] The light-emitting element according to [12], wherein the p-type layer contains a two-dimensional hole gas.

[14]According to the above [12]]Or [13]The light-emitting element, wherein the n-type contact layer contains a concentration at which the degeneracy occurs and is 4.0 × 10¹⁹cm^-3Si at the following concentrations.

[15] The light-emitting element according to any one of [12] to [14], wherein a portion of the n-electrode in contact with the first n-type contact layer and a portion of the p-electrode in contact with the second n-type contact layer are made of the same material.

[16] The light-emitting element according to the above [15], wherein the material is aluminum.

According to the present invention, a light-emitting element having an n-type contact layer made of AlGaN in which the resistance is effectively reduced by the degeneracy of the fermi level and the conduction band, and which is made of Si as a dopant, and a method for manufacturing the light-emitting element can be provided.

Further, according to the present invention, a light-emitting element which emits deep ultraviolet light, in which the contact resistance between the p-side electrode and the contact layer is low and the absorption of light by the contact layer is suppressed, can be provided.

In addition, according to the present invention, a deep ultraviolet light-emitting element using a tunnel junction can be provided, which suppresses absorption of light by an n-type layer and a p-type layer forming the tunnel junction.

Drawings

Fig. 1 is a vertical sectional view of a light-emitting element according to a first embodiment of the present invention.

Fig. 2 is a vertical sectional view of a light-emitting element according to a second embodiment of the present invention.

Fig. 3 is a vertical sectional view of a modification of the light-emitting element according to the second embodiment of the present invention.

Fig. 4 is a vertical sectional view of a light-emitting device including a light-emitting element according to a second embodiment of the present invention as a light source.

Fig. 5 is a vertical sectional view of a light-emitting element according to a third embodiment of the present invention.

Fig. 6 is a graph showing the relationship between the Al composition of the n-type contact layer and the resistivity.

Fig. 7 (a) to (c) are graphs showing the relationship between the Si concentration and the resistivity of the n-type contact layer.

Fig. 8 (a) to (c) are graphs showing temperature dependence of the resistivity, carrier concentration, and mobility of the n-type contact layer.

FIG. 9 is a graph showing the relationship between the V/III ratio of the source gas of the n-type contact layer and the resistivity.

Fig. 10 is a graph showing the relationship between the growth temperature and the resistivity of the n-type contact layer.

Fig. 11 (a) to (c) show spectra obtained by cathodoluminescence measurement of various n-type contact layers.

FIG. 12 is a graph showing the relationship between the Al content of the n-type contact layer and the transmittance of deep ultraviolet light having a wavelength of 280 nm.

Fig. 13 is a graph showing the relationship between the Al composition of the n-type contact layer and the resistivity.

Fig. 14 (a) to (c) are graphs showing the relationship between the Si concentration and the resistivity of the n-type contact layer.

Fig. 15 (a) to (c) are graphs showing temperature dependence of the resistivity, carrier concentration, and mobility of the n-type contact layer.

Fig. 16 shows spectra (CL spectra) obtained by cathodoluminescence measurement of each n-type contact layer.

Description of the symbols

1 light emitting element

10 base plate

11 buffer layer

12 n type contact layer

13 light-emitting layer

14 electron blocking layer

15 p type contact layer

16 transparent electrode

17 p electrode

18 n electrode

101. 102 light emitting element

110 substrate

111 buffer layer

112 n type contact layer

113 light emitting layer

114 current diffusion layer

1141 first AlGaN layer

1142 second AlGaN layer

1143 upper surface

1144 two-dimensional cavity gas

115 p type contact layer

116 p electrode

117 n electrode

118 passivation film

119 light reflecting layer

211 luminous element

210 base plate

211 buffer layer

212 n type contact layer

213 light-emitting layer

214 electron blocking layer

215 p type layer

216 n type contact layer

217 p electrode

218 n electrode

Detailed Description

[ first embodiment ]

(constitution of light emitting element)

Fig. 1 is a vertical sectional view of a light-emitting element 1 according to a first embodiment of the present invention. The light emitting element 1 is a flip-chip mounted Light Emitting Diode (LED), and includes: the organic light emitting diode comprises a substrate 10, a buffer layer 11 on the substrate 10, an n-type contact layer 12 on the buffer layer 11, a light emitting layer 13 on the n-type contact layer 12, an electron blocking layer 14 on the light emitting layer 13, a p-type contact layer 15 on the electron blocking layer 14, a transparent electrode 16 on the p-type contact layer 15, a p-electrode 17 connected with the transparent electrode 16, and an n-electrode 18 connected with the n-type contact layer 12.

The term "upper" in the structure of the light-emitting element 1 means "upper" when the light-emitting element 1 is placed in the direction shown in fig. 1, and is a direction from the substrate 10 toward the p-electrode 17.

The substrate 10 is a growth substrate made of sapphire. The thickness of the substrate 10 is, for example, 900 μm. As a material of the substrate 10, AlN, Si, SiC, ZnO, or the like may be used in addition to sapphire.

The buffer layer 11 has a structure in which 3 layers of a core layer, a low-temperature buffer layer, and a high-temperature buffer layer are sequentially stacked, for example. The nucleus layer is composed of undoped AlN which grows at a low temperature, and is a layer which becomes a nucleus for crystal growth. The thickness of the core layer is, for example, 10 nm. The low-temperature buffer layer is a layer composed of undoped AlN that is grown at a higher temperature than the core layer. The thickness of the low-temperature buffer layer is, for example, 0.3 μm. The high-temperature buffer layer is a layer composed of undoped AlN that is grown at a higher temperature than the low-temperature buffer layer. The thickness of the high-temperature buffer layer is, for example, 2.7 μm. By providing such a buffer layer 11, a reduction in the density of threading dislocations of AlN is achieved.

The light-emitting layer 13 is a layer laminated on the n-type contact layer 12. The light-emitting layer 13 is made of AlGaN, and preferably has a Multiple Quantum Well (MQW) structure. The Al component of the light-emitting layer 13 (Al component of the well layer in the case of the MQW structure) can be set according to a desired light-emitting wavelength, and is set to 35 to 45% when the light-emitting wavelength is about 280nm, for example. Here, the percentage of the Al component is a ratio of the Al content to a total of the Ga content and the Al content.

For example, the light-emitting layer 13 has an MQW structure in which the well layer is 2 layers, that is, a structure in which a first barrier layer, a first well layer, a second barrier layer, a second well layer, and a third barrier layer are stacked in this order. The first well layer and the second well layer are made of n-type AlGaN. The first barrier layer, the second barrier layer, and the third barrier layer are made of n-type AlGaN (including AlN having an Al composition of 100%) having an Al composition higher than that of the first well layer and the second well layer.

For example, the first well layer and the second well layer had an Al composition, a thickness, and a concentration of Si as a dopant of 40%, 2.4nm, and 9 × 10, respectively¹⁸/cm³. The first barrier layer and the second barrier layer had an Al content, a thickness, and a dopant concentration of Si of 55%, 19nm, and 9X 10, respectively¹⁸/cm³. The third barrier layer had an Al content, thickness and Si concentration of 55% as a dopant, and was 4nm and 5X 10¹⁸/cm³。

The n-type contact layer 12 is made of n-type AlGaN. The lower limit of the Al component of the n-type contact layer 12 is set to a lower limit of a range in which absorption of light emitted from the light-emitting layer 13 can be suppressed. If the Al composition of n-type contact layer 12 is larger than the Al composition of AlGaN constituting light-emitting layer 13 (the Al composition of the well layer when light-emitting layer 13 has the MQW structure) by 10% or more, absorption of light emitted from light-emitting layer 13 by n-type contact layer 12 can be effectively suppressed, and if it is larger by 15% or more, it can be more effectively suppressed. Therefore, the Al composition of the n-type contact layer 12 is preferably 10% or more, more preferably 15% or more larger than the Al composition of the light-emitting layer 13.

For example, when the Al content of the light-emitting layer 13 is 35 to 45%, light having a wavelength of about 280nm is emitted, and when the Al content of the n-type contact layer 12 is 50% or more, absorption can be effectively suppressed, and when the Al content is 55% or more, absorption can be more effectively suppressed.

The upper limit of the Al component of n-type contact layer 12 is set to an upper limit within a range in which an increase in resistance associated with an increase in the Al component can be suppressed. The resistance of AlGaN is almost constant at 70% or less when the Al composition is increased, but starts to increase when the Al composition exceeds 70%. Therefore, the Al content of the n-type contact layer 12 is set to 70% or less.

Therefore, as a preferable example when the light emitting element 1 is an ultraviolet light emitting element, the Al content of the n-type contact layer 12 is in a range of 50% to 70%. In this case, it is desirable that the n-type contact layer 12 have Al_xGa_1-xAnd N (0.5. ltoreq. x. ltoreq.0.7).

In addition, the n-type contact layer 12 contains Si in a concentration where the fermi level is degenerate with the conduction band. According to the non-patent documents "A.Wolos et al", "Properties of metal-insulator transition and electron spin relaxation in GaN: Si", PHYSICAL REVIEW B83,165206 (2011) ", it is said that in GaN containing Si as a dopant, the Si concentration is 1.6X 10¹⁸cm^-3Above this the fermi level is degenerate with the conduction band. Since AlGaN is considered to exhibit almost the same behavior as GaN, it is considered that the Si concentration in the n-type contact layer 12 is about 1.6 × 10¹⁸cm^-3When aboveThe fermi level will also be degenerate with the conduction band.

In addition, in order to suppress an increase in resistance associated with an increase in Si concentration, the concentration of Si contained in n-type contact layer 12 is set to 4.0 × 10¹⁹cm^-3The following. As described above, in AlGaN containing Si at a high concentration, although the fermi level is generally degenerated with the conduction band, the resistance cannot be effectively reduced due to the influence of recombination defects of group III holes and Si. However, when the n-type contact layer 12 is formed under the conditions such as the V/III ratio of the source gas according to the present embodiment, which will be described later, if the Si concentration is 4.0X 10¹⁹cm^-3Hereinafter, it is possible to suppress an increase in resistance which is considered to be caused by the influence of the recombination defect of the group III hole and Si.

The details of the defects of the recombination of the group III holes and Si are not clear, but there is a description that when Si does not enter the group III holes generated in the growth process of AlGaN and remains at other positions, Si cannot function as a donor (emits electrons), and 1 to 3 holes are emitted depending on the state, whereby the resistance increases.

According to the present embodiment, for example, by setting the Si concentration of the n-type contact layer 12 to 5 × 10¹⁸cm^-3～4×10¹⁹cm^-3In the range of (1), the growth temperature of the n-type contact layer 12 is set to 850 to 1100 ℃, and the V/III ratio of the source gas of the n-type contact layer 12, which will be described later, is set to 1000 to 3200, whereby the resistivity of the n-type contact layer 12 can be set to 5X 10^-2Omega cm or less. The lower limit of the resistivity of n-type contact layer 12 under the conditions of Si concentration, growth temperature, and V/III ratio of the source gas of n-type contact layer 12 is considered to be 1 × 10^-3Omega cm or so. The thickness of the n-type contact layer 12 is, for example, 500 to 3000 nm.

The electron blocking layer 14 is made of p-type AlGaN having a higher Al composition than the third barrier layer. Diffusion of electrons to the p-type contact layer 15 side is suppressed by the electron blocking layer 14. The Al content, thickness and Mg concentration as a dopant of the electron-blocking layer 14 are, for example, 80%, 25nm and 5X 10¹⁹/cm³。

The p-type contact layer 15 has a first p-type contact layer and a second p-type contact layerThe contact layer is laminated in this order. The first p-type contact layer and the second p-type contact layer are composed of p-type GaN. The thickness of the first p-type contact layer and the Mg concentration as a dopant are, for example, 700nm and 2X 10, respectively¹⁹/cm³. The thickness of the second p-type contact layer and the concentration of Mg as a dopant are, for example, 60nm and 1X 10, respectively²⁰/cm³。

A groove is provided in a partial region of the surface of the p-type contact layer 15. The groove penetrates through p-type contact layer 15 and light-emitting layer 13 to reach n-type contact layer 12, and n-electrode 18 is connected to the exposed surface of n-type contact layer 12 by the groove.

The transparent electrode 16 is made of a conductive oxide transparent to visible light, such as IZO, ITO, ICO, and ZnO. When the light emitted from the light-emitting layer 13 is ultraviolet light (light having a wavelength of 365nm or less), much of the light is absorbed by the p-type contact layer 15 made of GaN, and the light does not pass through the transparent electrode 16, so that the reflected light at the p-electrode 17 is not obtained. However, when the p-type contact layer 15 made of GaN as a thin film is used, or when the p-type contact layer 15 made of AlGaN is used, and when the transparent electrode 16 as a thin film is used, or when the transparent electrode 16 made of a material transparent to ultraviolet light is used, absorption of ultraviolet light by these can be suppressed, and therefore, the light output can be greatly improved. The p-electrode 17 is made of, for example, Ni/Au. The n-electrode 18 is made of, for example, Ti/Al/Ni, V/Al/Ru, or the like.

Note that the light emitting element 1 may be of a front mount type. The characteristic configuration of the n-type contact layer 12 and the like of the light-emitting element 1 can be applied to light-emitting elements other than LEDs such as laser diodes.

(method for manufacturing light emitting element)

An example of a method for manufacturing the light-emitting element 1 according to the first embodiment of the present invention will be described below. In each layer of the light-emitting element 1 formed by the vapor deposition method, for example, trimethyl gallium, trimethyl aluminum, and ammonia are used as the Ga raw material gas, the Al raw material gas, and the N raw material gas, respectively. For example, a silane gas and a bis (cyclopentadienyl) magnesium gas are used as the source gas of Si as an n-type dopant and as the source gas of Mg as a p-type dopant. As the carrier gas, for example, hydrogen or nitrogen is used. In the present embodiment, the growth temperature of each layer is the temperature of the heating heater of the film forming apparatus, and the surface temperature of the substrate 10 is lower than the temperature of the heating heater by about 100 ℃.

First, the substrate 10 is prepared, and the buffer layer 11 is formed thereon. In forming the buffer layer 11, first, a core layer made of AlN is formed by sputtering. The growth temperature is, for example, 880 ℃. Next, a low-temperature buffer layer and a high-temperature buffer layer made of AlN were sequentially formed on the core layer by the MOCVD method. Growth conditions of the low-temperature buffer layer are, for example: the growth temperature is 1090 ℃ and the growth pressure is 50 mbar. In addition, the growth conditions of the high-temperature buffer layer are, for example: the growth temperature was 1270 ℃ and the growth pressure 50 mbar.

Next, an n-type contact layer 12 made of AlGaN containing Si is formed on the buffer layer 11 by the MOCVD method. In the formation of the n-type contact layer 12, the V/III ratio of the source gas of the n-type contact layer 12 is set within the range of 1000 to 3200 in order to reduce the resistance of the n-type contact layer 12. Here, the V/III ratio is a ratio of the number of atoms in the source gas of the group III element (Ga, Al) and the group V element (N).

In the formation of n-type contact layer 12, the growth temperature of n-type contact layer 12 is preferably set to 1150 ℃. By setting the growth temperature to 1150 ℃ or less, an increase in resistance accompanying an increase in growth temperature can be suppressed. This is considered to be because the evaporation of the group III element, particularly Ga which is easily evaporated, is suppressed, and the excessive generation of the group III vacancies is suppressed, thereby suppressing the increase in the resistance due to the influence of the recombination defect of the group III vacancies and Si.

In the formation of the n-type contact layer 12, the growth temperature of the n-type contact layer 12 is preferably set to 850 ℃. When the growth temperature is less than 850 ℃, ammonia which is a raw material of the group V element N is hardly decomposed, so that the supply amount of ammonia must be increased and the V/III ratio must be set to be extremely high. Further, since the problem of mixing C from the group III material also occurs when the growth temperature is low, it is preferable to set the growth temperature to a temperature that can avoid the problem, for example, 850 ℃.

The growth pressure of the n-type contact layer 12 is set to 20 to 200mbar, for example.

Next, the light-emitting layer 13 is formed on the n-type contact layer 12 by the MOCVD method. The light-emitting layer 13 is formed by stacking a first barrier layer, a first well layer, a second barrier layer, a second well layer, and a third barrier layer in this order. The growth conditions of the light-emitting layer 13 are, for example: the growth temperature is 975 ℃ and the growth pressure is 400 mbar.

Next, the electron blocking layer 14 is formed on the light emitting layer 13 by the MOCVD method. The growth conditions of the electron blocking layer 14 are, for example: the growth temperature was 1025 ℃ and the growth pressure was 50 mbar.

Next, the p-type contact layer 15 is formed on the electron blocking layer 14 by the MOCVD method. The p-type contact layer 15 is formed by stacking a first p-type contact layer and a second p-type contact layer in this order. The growth conditions of the first p-type contact layer are, for example: the growth temperature is 1050 ℃ and the growth pressure is 200 mbar. The growth conditions of the second p-type contact layer are, for example: the growth temperature is 1050 ℃ and the growth pressure is 100 mbar.

Next, a predetermined region on the surface of p-type contact layer 15 is dry-etched to form a groove having a depth reaching n-type contact layer 12.

Next, the transparent electrode 16 is formed on the p-type contact layer 15. Next, p-electrode 17 is formed on transparent electrode 16, and n-electrode 18 is formed on n-type contact layer 12 exposed at the bottom surface of the trench. The transparent electrode 16, the p-electrode 17, and the n-electrode 18 are formed by sputtering, vapor deposition, or the like.

(Effect of the first embodiment)

According to the first embodiment of the present invention, the amount of recombination defects of group III holes and Si can be suppressed, and an n-type contact layer made of AlGaN, in which the resistance is effectively reduced by degeneracy of the fermi level and the conduction band, can be obtained. By lowering the resistance of the n-type contact layer, the output of the light-emitting element to a forward current can be increased.

[ second embodiment ]

(constitution of light emitting element)

Fig. 2 is a vertical sectional view of a light-emitting element 101 according to a second embodiment of the present invention. The light emitting element 101 is a flip chip mounted deep ultraviolet Light Emitting Diode (LED). Here, the deep ultraviolet refers to a wavelength region of 200 to 300 nm.

The light-emitting element 101 includes: the light emitting device includes a substrate 110, a buffer layer 111 on the substrate 110, an n-type contact layer 112 on the buffer layer 111, a light emitting layer 113 on the n-type contact layer 112, an electron blocking layer 120 on the light emitting layer 113, a current diffusion layer 114 on the electron blocking layer 120, a p-type contact layer 115 connected to a portion of an upper surface 1143 of the current diffusion layer 114, a p-electrode 116 connected to the p-type contact layer 115, and an n-electrode 117 connected to the n-type contact layer 112.

The term "upper" in the structure of the light-emitting element 101 refers to "upper" when the light-emitting element 101 is placed in the direction shown in fig. 2, and is a direction from the substrate 110 toward the p-electrode 116.

The substrate 110 is a growth substrate made of sapphire. The thickness of the substrate 110 is, for example, 900 μm. As a material of the substrate 110, AlN, Si, SiC, ZnO, or the like can be used in addition to sapphire.

The buffer layer 111 has a structure in which 3 layers of a core layer, a low-temperature buffer layer, and a high-temperature buffer layer are stacked in this order, for example. The nucleus layer is composed of undoped AlN which grows at a low temperature, and is a layer which becomes a nucleus for crystal growth. The thickness of the core layer is, for example, 10 nm. The low-temperature buffer layer is a layer composed of undoped AlN that is grown at a higher temperature than the core layer. The thickness of the low-temperature buffer layer is, for example, 0.3 μm. The high-temperature buffer layer is a layer composed of undoped AlN that is grown at a higher temperature than the low-temperature buffer layer. The thickness of the high-temperature buffer layer is, for example, 2.7 μm. By providing such a buffer layer 111, a reduction in the density of threading dislocations of AlN is achieved. The AlN constituting the buffer layer 111 may be n-type.

The light-emitting layer 113 is made of AlGaN, and preferably has a Multiple Quantum Well (MQW) structure. The Al component of the light-emitting layer 113 (Al component of the well layer in the case of having the MQW structure) can be set in accordance with a desired emission wavelength in the deep ultraviolet region (200 to 300nm), and for example, the emission wavelength is set to about 35 to 45% in the case of 270 to 290 nm. Here, the percentage of the Al component is a ratio of the Al content to a total of the Ga content and the Al content.

For example, the light-emitting layer 113 has an MQW structure in which the well layer is 2 layers, that is, a structure in which a first barrier layer, a first well layer, a second barrier layer, a second well layer, and a third barrier layer are stacked in this order. The first well layer and the second well layer are made of n-type AlGaN. The first barrier layer, the second barrier layer, and the third barrier layer are made of n-type AlGaN (including AlN having an Al composition of 100%) having an Al composition higher than that of the first well layer and the second well layer.

The n-type contact layer 112 is made of n-type AlGaN. The lower limit of the Al component of the n-type contact layer 112 is set to a lower limit in a range in which absorption of light emitted from the light-emitting layer 113 can be suppressed. For example, if the Al content of the n-type contact layer 112 is 50% or more, absorption of deep ultraviolet light having a wavelength of 270 to 290nm and light having a longer wavelength than that can be suppressed, and if it is 55% or more, absorption can be more effectively suppressed.

The upper limit of the Al component of n-type contact layer 112 is set to an upper limit within a range in which an increase in resistance associated with an increase in the Al component can be suppressed. The resistance of AlGaN is almost constant at 70% or less when the Al composition is increased, but starts to increase when the Al composition exceeds 70%. Therefore, the Al content of n-type contact layer 112 is preferably set to 70% or less.

Therefore, as a preferable example, the Al content of n-type contact layer 112 is in the range of 50% to 70%. In this case, it is desirable that the n-type contact layer 112 have Al_xGa_1-xAnd N (0.5. ltoreq. x. ltoreq.0.7).

In addition, the n-type contact layer 112 preferably contains Si in a concentration where the fermi level is degenerate (overlapping) with the conduction band. Semiconductors whose fermi level is degenerate with the conduction band behave like metals with reduced resistance.

According to the non-patent documents "A.Wolos et al", "Properties of metal-insulator transition and electron spin relaxation in GaN: Si", PHYSICALREVIEW B83,165206, 165206(2011) ", in GaN containing Si as a dopant, the Si concentration is 1.6X 10¹⁸cm^-3Above, the fermi level is degenerate with the conduction band. Since AlGaN is considered to exhibit almost the same behavior as GaN, it is considered that the Si concentration in the n-type contact layer 112 is about 1.6 × 10¹⁸cm^-3Above, the fermi level will also be degenerate with the conduction band.

On the other hand, in n-type AlGaN in which Si is used as a dopant, if the Si concentration is increased, the resistance decreases as in a general semiconductor until a certain concentration, but if the concentration exceeds a certain concentration, the resistance starts to increase instead. Therefore, in order to suppress an increase in resistance associated with an increase in Si concentration, it is preferable to set the Si concentration in n-type contact layer 112 to 4.0 × 10¹⁹cm^-3The following.

It is considered that the increase in resistance accompanying the increase in Si concentration in n-type AlGaN using Si as a dopant is caused by the generation of a recombination defect of a group III hole and Si when the Si concentration exceeds a certain concentration. The details of the defects of recombination of group III holes and Si are not clear, but there is a statement that: when Si does not enter group III holes generated during the growth of AlGaN and remains in other positions, Si cannot function as a donor (emits electrons), but 1 to 3 holes are emitted depending on the state, thereby increasing the resistance.

The thickness of the n-type contact layer 112 is, for example, 0.3 to 3 μm.

The electron blocking layer 120 is made of p-type AlGaN having a higher Al composition than the third barrier layer of the light emitting layer 113. The diffusion of electrons to the current diffusion layer 114 side can be suppressed by the electron blocking layer 120. The Al content, thickness and Mg concentration as dopant of the electron blocking layer 120 are, for example, 80% or more, 25nm and 1X 10¹⁸～1×10²⁰cm^-3。

The current diffusion layer 114 is made of AlGaN containing a two-dimensional hole gas 1144. The current diffusion layer 114 includes a p-type first AlGaN layer 1141 and a p-type or i-type second AlGaN layer 1142 directly provided on the first AlGaN layer 1141, and the second AlGaN layer 1142 includes a two-dimensional hole gas 1144 in the vicinity of the interface with the first AlGaN layer 1141.

The Al composition of the first AlGaN layer 1141 is higher than that of the second AlGaN layer 1142. In addition, in order to suppress absorption of deep ultraviolet light emitted from the light-emitting layer 113, the Al composition of the first AlGaN layer 1141 and the second AlGaN layer 1142 is preferably 30% or more.

For example, the Al composition of the first AlGaN layer 1141 is in a range of 50% to 70%, and the Al composition of the second AlGaN layer 1142 is in a range of 30% to 50%. At this time, it is desirable that the first AlGaN layer 1141 have Al_xGa_1-xN (0.5. ltoreq. x. ltoreq.0.7), and the second AlGaN layer 1142 has Al_xGa_1-xAnd N (0.3. ltoreq. x. ltoreq.0.5). In the case where the thickness of the second AlGaN layer 1142 is large (for example, about 50nm or more), it is necessary to consider that deep ultraviolet light emitted from the light-emitting layer 113 is absorbed by the second AlGaN layer 1142, and therefore, it is preferable that the Al content of the second AlGaN layer 1142 be 40% or more.

By laminating the second AlGaN layer 1142 in a state where the band gap energy is larger than that of the second AlGaN layer 1142 and is 5X 10¹⁷cm^-3In the first AlGaN layer 1141 doped with Mg in the above concentration, the fermi level and the valence band are degenerated in a region where the energy band is bent in the vicinity of the interface between the second AlGaN layer 1142 and the first AlGaN layer 1141, and a two-dimensional hole gas 1144 is generated.

Since the current diffusion layer 114 contains the two-dimensional hole gas 1144, holes are transferred with high mobility in the two-dimensional hole gas 1144, and thus current is efficiently diffused in the in-plane direction of the current diffusion layer 114. Here, the two-dimensional hole gas can be observed as a high-concentration p-type region by cross-sectional scm (scanning Capacitance microscope). That is, if a high concentration p-type region is observed in the vicinity of the interface between the second AlGaN layer 1142 and the first AlGaN layer 1141, it can be determined that two-dimensional hole gas is generated.

The thickness of the first AlGaN layer 1141 is, for example, 5 to 50 nm. The thickness of the second AlGaN layer 1142 is, for example, 5 to 100 nm.

p-type contact layer 115 is made of p-type GaN or p-type AlGaN having 35% or less of Al component, and preferably comprises GaN or Al_xGa_1-xAnd N (x is less than or equal to 0.35). Therefore, the contact voltage of the p-type contact layer 115 with the p-electrode 116 can be suppressed low.

On the other hand, since AlGaN having a composition of 35% or less of GaN and Al has a high deep ultraviolet light absorptance, light emitted from the light-emitting layer 113 and directed toward the p-type contact layer 115 is strongly absorbed by the p-type contact layer 115. For example, when the Al content of p-type contact layer 115 is 35%, the transmittance of light having a wavelength of 280nm is about 90% when the thickness is 20nm, and light having a wavelength of about 290nm or less is almost absorbed when the thickness is sufficiently large. When the Al content of p-type contact layer 115 is 30%, the transmittance of light having a wavelength of 280nm is about 80% when the thickness is 20nm, and light having a wavelength of about 310nm or less is almost absorbed when the thickness is sufficiently large.

Therefore, in the light-emitting element 101, the p-type contact layer 115 is formed only on a part of the upper surface 1143 of the current diffusion layer 114, whereby the absorption of deep ultraviolet light emitted from the light-emitting layer 113 by the p-type contact layer 115 is suppressed to be low. In order to more effectively suppress absorption of ultraviolet light by p-type contact layer 115, the area of upper surface 1143 in contact with p-type contact layer 115 is preferably 80% or less, more preferably 50% or less, of the area of the entire upper surface 1143.

Note that when a ps Substrate (Patterned Sapphire Substrate) having a concave-convex pattern on the surface is used as the Substrate 110, the effect of the present invention of suppressing the absorption of light by the p-type contact layer 115 is particularly advantageous because light going back and forth in the light-emitting element 101 is increased.

The p-type contact layer 115 is connected to the current diffusion layer 114 only in a part of the upper surface 1143, but the current diffusion layer 114 containing the two-dimensional hole gas 1144 efficiently diffuses the current in the in-plane direction, so that the uniformity of the light emission intensity in the light-emitting layer 113 can be ensured. In order to further improve the uniformity of the in-plane emission intensity of light-emitting layer 113, the area of upper surface 1143 in contact with p-type contact layer 115 is preferably 40% or more of the area of the entire upper surface 1143.

The thickness of the p-type contact layer 115 is, for example, 4 to 30 nm.

The p-electrode 116 is made of, for example, Ni/Au. The n-electrode 117 is made of, for example, Ti/Al/Ni, V/Al/Ru, or the like.

As shown in fig. 2, it is preferable that at least a part, more preferably all, of the region of the upper surface 1143 of the current diffusion layer 114 other than the region to which the p-type contact layer 115 is connected is covered with SiO₂And a passivation film 118 made of an insulating material such as SiN. By using the passivation film 118, generation of a surface leakage current flowing on the upper surface 1143 of the current diffusion layer 114 can be suppressed, and a current can be efficiently flowed in the two-dimensional hole gas 1144.

The light-reflecting layer 119 is preferably provided above a region other than the region of the upper surface 1143 of the current diffusion layer 114 that contacts the p-type contact layer 115. The light reflecting layer 119 is made of a material having a high reflectance to deep ultraviolet light, such as aluminum, rhodium, or ruthenium. By reflecting light emitted from the light-emitting layer 113 using the light-reflecting layer 119, the light extraction efficiency of the light-emitting element 101 can be improved. The light reflecting layer 119 may be embedded in the passivation film 118 as shown in fig. 2, for example.

The characteristic configuration of the current diffusion layer 114, the p-type contact layer 115, and the like of the light-emitting element 101 can be applied to light-emitting elements other than LEDs, such as vertical laser diodes of VCSEL type and the like.

(method for manufacturing light emitting element)

An example of a method for manufacturing the light-emitting element 101 according to the second embodiment of the present invention will be described below. In each layer of the light-emitting element 101 formed by the vapor deposition method, for example, trimethyl gallium, trimethyl aluminum, and ammonia are used as the Ga material gas, the Al material gas, and the N material gas, respectively. For example, a silane gas and a bis (cyclopentadienyl) magnesium gas are used as the source gas of Si as an n-type dopant and as the source gas of Mg as a p-type dopant. As the carrier gas, for example, hydrogen or nitrogen is used.

First, the substrate 110 is prepared, and the buffer layer 111 is formed thereon. In forming the buffer layer 111, first, a core layer made of AlN is formed. For example, a nuclear layer is formed by MOCVD at a growth temperature of 880 ℃. In addition, the core layer may be formed by a sputtering method. Next, a low-temperature buffer layer and a high-temperature buffer layer made of AlN were sequentially formed on the core layer by the MOCVD method. The growth conditions of the low-temperature buffer layer are, for example: the growth temperature is 1090 ℃ and the growth pressure is 50 mbar. In addition, the growth conditions of the high-temperature buffer layer are, for example: the growth temperature was 1270 ℃ and the growth pressure 50 mbar.

Next, an n-type contact layer 112 made of AlGaN containing Si is formed on the buffer layer 111 by the MOCVD method. The growth conditions of the n-type contact layer 112 are, for example: the growth temperature is 980 ℃ and the growth pressure is 50 mbar.

Next, the light-emitting layer 113 is formed on the n-type contact layer 112 by the MOCVD method. The light-emitting layer 113 is formed by stacking a first barrier layer, a first well layer, a second barrier layer, a second well layer, and a third barrier layer in this order. The growth conditions of the light-emitting layer 113 are, for example: the growth temperature is 975 ℃ and the growth pressure is 400 mbar.

Next, the electron blocking layer 120 is formed on the light emitting layer 113 by the MOCVD method. The growth conditions of the electron blocking layer 120 are, for example: the growth temperature is 1000 ℃ and the growth pressure is 50 mbar.

Next, a first AlGaN layer 1141 and a second AlGaN layer 1142 constituting the current diffusion layer 114 are formed on the electron blocking layer 120 by an MOCVD method. The growth conditions of the first AlGaN layer 1141 are, for example: the growth temperature is 950-1000 deg.C (980 deg.C as a typical example), and the growth pressure is 50 mbar. The growth conditions of the second AlGaN layer 1142 are, for example: the growth temperature is 950-1000 deg.C (980 deg.C as a typical example), and the growth pressure is 50 mbar.

Next, the p-type contact layer 115 is formed on the current diffusion layer 114 by the MOCVD method. The growth conditions of the p-type contact layer 115 are, for example: the growth temperature is 1000-1100 deg.C (1050 deg.C as a typical example), and the growth pressure is 50 mbar.

Next, a predetermined region on the surface of p-type contact layer 115 is subjected to two-step dry etching, and grooves for connecting n-electrode 117 to the depth of n-type contact layer 112 and patterning of p-type contact layer 115 on current diffusion layer 114 are performed.

Next, a p-electrode 116 is formed on the p-type contact layer 115, and an n-electrode 117 is formed on the n-type contact layer 112 exposed at the bottom surface of the trench. The p-electrode 116 and the n-electrode 117 are formed by sputtering, vapor deposition, or the like.

(modification example)

Fig. 3 is a vertical sectional view of a light-emitting element 102 as a modification of the light-emitting element 101 according to the second embodiment of the present invention. The light-emitting element 102 is different from the light-emitting element 101 in the planar shape of the p-type contact layer 115.

The p-type contact layer 115 of the light-emitting element 102 has a ring-shaped planar shape. Further, a region inside the region of the upper surface 1143 of the current diffusion layer 114 to which the ring-shaped p-type contact layer 115 is connected is covered with the passivation film 118, and the light reflection layer 119 is provided on the passivation film 118.

As shown in the example of the light-emitting element 102, the planar shape of the p-type contact layer 115 of the light-emitting element according to the present embodiment can be changed to, for example, a circular shape, a ring shape, a mesh shape, or the like as appropriate depending on the application of the light-emitting element or the like.

(application example)

Fig. 4 is a vertical sectional view of a light-emitting device 103 having the light-emitting element 101 according to the second embodiment of the present invention as a light source. The light-emitting device 103 is a light-emitting device having a multilayer wiring structure called a build-up (built up) structure, and is an example of a light-emitting device having the light-emitting element 101 as a light source.

In the light-emitting device 103, the p-electrodes 116 of the plurality of light-emitting elements 101 are connected to the p-pad electrode 133 via the bonding electrode 131, and the n-electrodes 117 of the plurality of light-emitting elements 101 are connected to the n-pad electrode 134 via the bonding electrode 132. Then, a voltage is applied between the p-pad electrode 133 and the n-pad electrode 134, whereby the plurality of light-emitting elements 101 emit light.

In the light-emitting device 103, the

bonding electrodes

131 and 132 are wired inside the insulating

layers

135 and 136, and the light-reflecting layer 119 is embedded in the insulating layer 135 covering the light-emitting element 101.

(Effect of the second embodiment)

According to the second embodiment of the present invention, it is possible to provide a light-emitting element in which the contact resistance between the p-side electrode and the contact layer is low and the absorption of light by the contact layer is suppressed by reducing the area of the p-type contact layer having a high deep ultraviolet light absorption rate and efficiently diffusing a current in the in-plane direction by the diffusion layer.

[ third embodiment ]

(constitution of light emitting element)

Fig. 5 is a vertical sectional view of a light-emitting element 201 according to a third embodiment of the present invention. The light emitting element 201 is a flip chip mounted deep ultraviolet Light Emitting Diode (LED). Here, the deep ultraviolet refers to a wavelength region of 200 to 300 nm.

The light-emitting element 201 includes: a substrate 210, a buffer layer 211 on the substrate 210, an n-type contact layer 212 on the buffer layer 211, a light emitting layer 213 on the n-type contact layer 212, an electron blocking layer 214 on the light emitting layer 213, a p-type layer 215 on the electron blocking layer 214, an n-type contact layer 216 on the p-type layer 215, a p-electrode 217 connected to the n-type contact layer 216, and an n-electrode 218 connected to the n-type contact layer 212.

The term "upper" in the structure of the light-emitting element 201 means "upper" when the light-emitting element 201 is placed in the direction shown in fig. 5, and is a direction from the substrate 210 to the p-electrode 217.

The substrate 210 is a growth substrate made of sapphire. The thickness of the substrate 210 is, for example, 900 μm. As a material of the substrate 210, AlN, Si, SiC, ZnO, or the like can be used in addition to sapphire.

The buffer layer 211 has a structure in which 3 layers of a core layer, a low-temperature buffer layer, and a high-temperature buffer layer are sequentially stacked, for example. The nucleus layer is composed of undoped AlN which grows at a low temperature, and is a layer which becomes a nucleus for crystal growth. The thickness of the core layer is, for example, 10 nm. The low-temperature buffer layer is a layer composed of undoped AlN that is grown at a higher temperature than the core layer. The thickness of the low-temperature buffer layer is, for example, 0.3 μm. The high-temperature buffer layer is a layer composed of undoped AlN that is grown at a higher temperature than the low-temperature buffer layer. The thickness of the high-temperature buffer layer is, for example, 2.7 μm. By providing such a buffer layer 211, a reduction in the density of threading dislocations of AlN is achieved.

The light-emitting layer 213 is made of AlGaN, and preferably has a Multiple Quantum Well (MQW) structure. The Al component of the light-emitting layer 213 (Al component of the well layer in the case of having the MQW structure) can be set in accordance with a desired emission wavelength in the deep ultraviolet region (200 to 300nm), and is set to about 40 to 50% in the case of an emission wavelength of 270 to 290nm, for example. Here, the percentage of the Al component is a ratio of the Al content to a total of the Ga content and the Al content.

For example, the light-emitting layer 213 has an MQW structure in which the well layer is 2 layers, that is, a structure in which a first barrier layer, a first well layer, a second barrier layer, a second well layer, and a third barrier layer are stacked in this order. The first well layer and the second well layer are made of n-type AlGaN. The first barrier layer, the second barrier layer, and the third barrier layer are made of n-type AlGaN (including AlN having an Al composition of 100%) having an Al composition higher than that of the first well layer and the second well layer.

For example, the first well layer and the second well layer had an Al composition, a thickness, and a concentration of Si as a dopant of 40%, 2.4nm, and 9 × 10, respectively¹cm^-3. The first barrier layer and the second barrier layer had an Al content, a thickness, and a dopant concentration of Si of 55%, 19nm, and 9X 10, respectively¹⁸cm^-3. The third barrier layer had an Al content, thickness and Si concentration of 55% as a dopant, and was 4nm and 5X 10¹⁸cm^-3。

The n-type contact layer 212 and the n-type contact layer 216 are made of n-type AlGaN. Further, in order to suppress absorption of deep ultraviolet light emitted from the light emitting layer 213, the Al composition of the n-type contact layer 212 and the n-type contact layer 216 is preferably higher than that of the light emitting layer 213, and is preferably in the range of, for example, 50% to 70%. In this case, it is desirable that the n-type contact layer 212 and the n-type contact layer 216 have Al_xGa_1-xAnd N (0.5. ltoreq. x. ltoreq.0.7).

If the Al content of the n-type contact layer 212 and the n-type contact layer 216 is 50% or more, high transmittance can be secured for deep ultraviolet light having a wavelength of 270 to 290nm and light having a longer wavelength than that. Further, if the Al content of n-type contact layer 212 and n-type contact layer 216 is 55% or more, a higher transmittance can be ensured, and if it is 60% or more, a further higher transmittance can be ensured.

Further, if the Al content of n-type contact layer 212 and n-type contact layer 216 is 70% or less, the resistance can be suppressed to be low. The resistance of AlGaN is almost constant at 70% or less when the Al composition is increased, but starts to increase when the Al composition exceeds 70%. Therefore, the Al composition of the n-type contact layer 212 and the n-type contact layer 216 is set to 70% or less.

On the other hand, in order to allow carriers to efficiently pass between the n-type contact layer 216 and the p-type layer 215, the Al component of the n-type contact layer 216 is preferably as low as possible, and when the passing of carriers is emphasized, the Al component of the light-emitting layer 213 is preferably set to be lower than the Al component of the light-emitting layer within a range in which the absorption of deep ultraviolet light is suppressed to some extent. Therefore, the Al content of n-type contact layer 216 is set to, for example, within a range of 40% to 70%. For the tunnel junction of the n-type contact layer 216 and the p-type layer 215, it is described below.

In addition, the n-type contact layer 212 and the n-type contact layer 216 contain Si in a concentration where the fermi level is degenerate (overlapping) with the conduction band. Semiconductors whose fermi level is degenerate with the conduction band behave like metals with reduced resistance.

According to the non-patent documents "A.Wolos et al," Properties of metal-insulator transition and electron spin relaxation in GaN: Si ", PHYSICALREVIEW B83,165206, 165206 (2011)", it is said that in GaN containing Si as a dopant, the Si concentration is 1.6X 10¹⁸cm^-3Above this the fermi level is degenerate with the conduction band. Since AlGaN is considered to exhibit almost the same behavior as GaN, it is considered that the n-type contact layer 212 and the n-type contact layer 216 have an Si concentration of about 1.6 × 10¹⁸cm^-3Above, the fermi level will also be degenerate with the conduction band.

On the other hand, in n-type AlGaN in which Si is used as a dopant, if the Si concentration is increased, the resistance decreases as in a general semiconductor until a certain concentration, but if the concentration exceeds a certain concentration, the resistance starts to increase instead. Therefore, in order to suppress an increase in resistance associated with an increase in Si concentration, Si contained in n-type contact layer 212 and n-type contact layer 216 is preferably usedThe concentration was set at 4.0X 10¹⁹cm^-3The following.

It is considered that the increase in resistance accompanying the increase in Si concentration in n-type AlGaN using Si as a dopant is caused by the generation of a recombination defect of a group III hole and Si when the Si concentration exceeds a certain concentration. The details of the defects of the recombination of the group III holes and Si are not clear, but there is a case where Si does not enter the group III holes generated in the growth process of AlGaN and remains at other positions, Si cannot function as a donor (emits electrons), and 1 to 3 holes are emitted depending on the state, thereby increasing the resistance.

The thickness of the n-type contact layer 212 is, for example, 500 to 2000 nm. The thickness of the n-type contact layer 216 is, for example, 25 to 200 nm.

The electron blocking layer 214 is a layer for suppressing diffusion of electrons to the n-type contact layer 216 side, and is made of, for example, undoped AlN. The thickness of the electron blocking layer 214 is, for example, 2 nm.

The p-type layer 215 is made of p-type AlGaN, and has a structure in which, for example, a p-type electron blocking layer and a p-type clad layer are stacked in this order. When the p-type electron blocking layer is composed of AlGaN, the p-type cladding layer is composed of AlGaN or GaN having a lower Al composition than the p-type electron blocking layer, and when the p-type electron blocking layer is composed of AlN, the p-type cladding layer is composed of AlGaN. The thickness of the p-type electron blocking layer is, for example, 10 to 50 nm. The thickness of the p-type cladding layer is, for example, 2 to 200 nm.

For example, when the p-type electron-blocking layer and the p-type cladding layer are made of AlGaN, the Al composition, the thickness, and the Mg concentration as a dopant of the p-type electron-blocking layer are, for example, 80%, 25nm, and 1 × 10%, respectively²⁰cm^-3. The Al content, thickness and Mg concentration as a dopant of the p-type clad layer are, for example, 35%, 5nm and 1X 10¹⁹cm^-3。

In order to suppress absorption of deep ultraviolet light emitted from the light-emitting layer 213, it is preferable that the Al composition of the p-type electron-blocking layer and the p-type cladding layer is higher than that of the light-emitting layer 213. In this case, the Al component of the p-type clad layer is preferably 50% or more, for example, 50 to 60%.

On the other hand, in order to allow carriers to efficiently pass between the n-type contact layer 216 and the p-type layer 215, the Al components of the p-type electron blocking layer and the p-type cladding layer are preferably as low as possible, and when importance is given to the passing of carriers, the Al component of the p-type cladding layer may be set to be lower than the Al component of the light-emitting layer 213 within a range in which the absorption of deep ultraviolet light is suppressed to some extent. For the tunnel junction of the n-type contact layer 216 and the p-type layer 215, it is described below.

An n-type contact layer 216 whose fermi level is degenerate with the conduction band forms a tunnel junction with the p-type layer 215. In the region where the energy band near the interface between the p-type layer 215 and the n-type contact layer 216 is bent, n-type and p-type carriers are distributed at high concentration, and therefore when a forward voltage is applied between the p-electrode 217 and the n-electrode 218, electrons migrate from the p-type layer 215 to the n-type contact layer 216 across the potential barrier, and the light-emitting element 201 emits light.

Further, when two-dimensional hole gas is generated in the vicinity of the interface between p-type layer 215 and n-type contact layer 216 due to degeneracy of the fermi level and the valence band, the potential barrier between p-type layer 215 and n-type contact layer 216 becomes thinner, tunneling is likely to occur, and the operating voltage of light-emitting element 201 can be reduced.

In order to form the two-dimensional hole gas, for example, a stack of different first layers having an Al component of 10% or more and second layers thereon is used as the p-type layer 215, each of which is made of p-type AlN, AlGaN, or AlGaInN. At this time, when the Al composition of the second layer is made larger than the Al composition of the first layer, electron boiling occurs at the interface between the first layer and the second layer, while hole boiling occurs at the interface between the second layer and the n-type contact layer 216, thereby forming a two-dimensional hole gas. The p-type layer 215 may have a structure (superlattice structure) in which a plurality of thin first layers and second layers are alternately stacked. In this case, two-dimensional hole gas may be formed near each interface between the first layer and the second layer. In this case, the Al content of either the first layer or the second layer may be increased. Here, in order to increase the carrier injection amount into the light-emitting layer 213, Mg is preferably doped in the p-type layer 215.

Note that the two-dimensional hole gas can be observed as a high-concentration p-type region by cross-sectional scm (scanning Capacitance microscope). That is, if a high concentration p-type region is observed in the vicinity of the interface between p-type layer 215 and n-type contact layer 216, it can be determined that two-dimensional hole gas is generated.

A groove is provided in a partial region of the surface of the n-type contact layer 216. The groove penetrates through n-type contact layer 216, p-type layer 215, and light-emitting layer 213, reaches n-type contact layer 212, and n-electrode 218 is connected to the exposed surface of n-type contact layer 212 by the groove.

In the light-emitting element 201, the n-type contact layer 212 connected to the n-electrode 218 and the n-type contact layer 216 connected to the p-electrode 217 are each formed of n-type AlGaN. Therefore, the same substance can be used for the material of the portion of the n-electrode 218 in contact with the n-type contact layer 212 and the portion of the p-electrode 217 in contact with the n-type contact layer 216. When the p-electrode 217 and the n-electrode 218 are each made of a single material, the same material can be used for the n-electrode 218 and the p-electrode 217.

Therefore, as in the case of the n-electrode 218, aluminum having a high reflectance to deep ultraviolet light may be used for the p-electrode 217. Therefore, aluminum is preferably used as a material for a portion of the n-electrode 218 in contact with the n-type contact layer 212 and a portion of the p-electrode 217 in contact with the n-type contact layer 216.

The p-electrode 217 and the n-electrode 218 are made of, for example, V/Al/NiAu, V/Al/Ru/Au. In this case, the V layer is preferably as thin as possible in order to increase the reflectance.

Since p-type AlGaN cannot make ohmic contact with aluminum having a low work function, aluminum cannot be used as a material for a p-electrode when a p-electrode is connected to a contact layer made of p-type AlGaN as in a conventional normal light-emitting element.

Note that the characteristic configuration of the n-type contact layer 216 and the like of the light-emitting element 201 can be applied to light-emitting elements other than LEDs such as laser diodes.

(method for manufacturing light emitting element)

An example of a method for manufacturing the light-emitting element 201 according to the third embodiment of the present invention will be described below. In each layer of the light-emitting element 201 formed by the vapor deposition method, for example, trimethyl gallium, trimethyl aluminum, and ammonia are used as the Ga material gas, the Al material gas, and the N material gas, respectively. For example, a silane gas and a bis (cyclopentadienyl) magnesium gas are used as the source gas of Si as an n-type dopant and as the source gas of Mg as a p-type dopant. As the carrier gas, for example, hydrogen or nitrogen is used.

First, a substrate 210 is prepared, and a buffer layer 211 is formed thereon. In forming the buffer layer 211, a core layer made of AlN is first formed by sputtering. The growth temperature is, for example, 880 ℃. Next, a low-temperature buffer layer and a high-temperature buffer layer made of AlN were sequentially formed on the core layer by the MOCVD method. The growth conditions of the low-temperature buffer layer are, for example: the growth temperature is 1090 ℃ and the growth pressure is 50 mbar. In addition, the growth conditions of the high-temperature buffer layer are, for example: the growth temperature was 1270 ℃ and the growth pressure 50 mbar.

Next, an n-type contact layer 212 made of AlGaN containing Si is formed on the buffer layer 211 by the MOCVD method. The growth conditions of the n-type contact layer 212 are, for example: the growth temperature is 980 ℃ and the growth pressure is 50 mbar.

In order to suppress an increase in the resistance of the n-type contact layer 212, the V/III ratio of the source gas of the n-type contact layer 212 is preferably set within a range of 1000 to 3200, and the growth temperature is preferably set to 1100 ℃. Here, the V/III ratio is a ratio of the number of atoms in the source gas of the group III element (Ga, Al) and the group V element (N). Further, since ammonia as a raw material of N is easily decomposed, it is preferable that the growth temperature is set to 850 ℃ or higher. The growth pressure of the n-type contact layer 212 is set to 20 to 200mbar, for example. When the growth temperature of n-type contact layer 212 is set to be low (approximately 850 ℃), the V/III ratio of the source gas is preferably set to be larger than the above range, for example, to approximately 10000, in order to suppress the capture of C. If C is taken out by the n-type contact layer 212, C acts as an acceptor to compensate carriers, and since C increases impurity scattering and decreases carrier mobility, the n-type contact layer 212 may have a high resistance.

Next, the light emitting layer 213 is formed on the n-type contact layer 212 by the MOCVD method. The light-emitting layer 213 is formed by stacking a first barrier layer, a first well layer, a second barrier layer, a second well layer, and a third barrier layer in this order. The growth conditions of the light emitting layer 213 are, for example: the growth temperature is 975 ℃ and the growth pressure is 400 mbar.

Next, the electron blocking layer 214 is formed on the light emitting layer 213 by the MOCVD method. The growth conditions of the electron blocking layer 214 are, for example: the growth temperature is 975 ℃ and the growth pressure is 400 mbar.

Next, a p-type layer 215 is formed on the electron blocking layer 214 by the MOCVD method. The p-type layer 215 is formed by stacking a p-type electron blocking layer and a p-type cladding layer in this order. The growth conditions of the p-type electron blocking layer are, for example: the growth temperature was 1025 ℃ and the growth pressure was 50 mbar. The growth conditions of the p-type cladding layer are, for example: the growth temperature is 980 ℃ and the growth pressure is 50 mbar.

After the p-type layer 215 is formed, annealing is preferably performed to remove hydrogen from the p-type layer 215 in order to activate Mg contained in the p-type layer 215.

Next, an n-type contact layer 216 is formed on the p-type layer 215 by the MOCVD method. The growth conditions of the n-type contact layer 216 are, for example: the growth temperature is 980 ℃ and the growth pressure is 50 mbar.

In addition, similarly to n-type contact layer 212, in order to suppress an increase in the electrical resistance of n-type contact layer 212, it is preferable to set the V/III ratio of the source gas of n-type contact layer 212 within the range of 1000 to 3200, and to set the growth temperature to 1100 ℃. In addition, in order to easily decompose ammonia as a raw material of N, the growth temperature is preferably set to 850 ℃ or higher. The growth pressure of the n-type contact layer 212 is set to 20 to 200mbar, for example.

Here, when hydrogen is removed from the p-type layer 215 by the annealing treatment, the growth temperature of the n-type contact layer 216 is preferably set to 900 ℃ or lower in order to suppress hydrogen from entering the p-type layer 215 again and deactivate Mg.

Next, a predetermined region on the surface of n-type contact layer 216 is dry-etched to form a groove reaching the depth of n-type contact layer 212.

Next, a p-electrode 217 is formed on the n-type contact layer 216, and an n-electrode 218 is formed on the n-type contact layer 212 exposed at the bottom surface of the trench. The p-electrode 217 and the n-electrode 218 are formed by sputtering, evaporation, or the like.

(Effect of the third embodiment)

According to the third embodiment of the present invention, a tunnel junction structure in which absorption of deep ultraviolet light is suppressed can be formed by using the n-type contact layer 216 made of AlGaN having a high Al composition in which the fermi level is degenerated with the conduction band. Further, by using the n-type contact layer 216 as a contact layer of the p-electrode 217, a material having a high reflectance to deep ultraviolet light, such as aluminum having a low work function, can be used as the material of the p-electrode 217.

Therefore, a large amount of light emitted from the light-emitting layer 213 and transmitted to the p-electrode 217 side is not absorbed by the n-type contact layer 216, but is transmitted, efficiently reflected by the p-electrode 217, and extracted from the substrate 210 side, so that the light-emitting element 201 has high light extraction efficiency.

Example 1

The evaluation results of the characteristics of the n-type contact layer 12 according to the first embodiment will be described below. In this example, n-type contact layers 12 were formed on a substrate 10 via a buffer layer 11 under various conditions described later, and these n-type contact layers 12 were evaluated. Table 1 below shows the composition and growth conditions of the substrate 10, the buffer layer 11, and the n-type contact layer 12 according to the present example.

[ Table 1]

In this example, the resistivity, carrier concentration, and mobility of the n-type contact layer 12 were measured by hole effect measurement, and the Si concentration was measured by Secondary Ion Mass Spectrometry (SIMS).

Fig. 6 is a graph showing the relationship between the Al composition and the resistivity of n-type contact layer 12. Fig. 6 shows that if the Al composition of the n-type contact layer 12 exceeds about 70%, the resistance increases. Table 2 below shows the numerical values of the plotted points in fig. 6, and the growth temperature of n-type contact layer 12 and the V/III ratio of the source gas for each plotted point.

[ Table 2]

Fig. 7 (a) to (c) are graphs showing the relationship between the Si concentration and the resistivity of n-type contact layer 12. The growth temperature of n-type contact layer 12 and the V/III ratio of the source gas in FIG. 7 (a) were 1013 ℃ and 1058, respectively. The growth temperature of n-type contact layer 12 and the V/III ratio of the source gas in FIG. 7 (b) were 1013 ℃ and 1587, respectively. The growth temperature of n-type contact layer 12 and the V/III ratio of the source gas in FIG. 7(c) were 1083 ℃ and 1058, respectively. FIGS. 7 (a) to (c) show that if the Si concentration of the n-type contact layer 12 exceeds about 4.0X 10¹⁹cm^-3The resistance increases. The numerical values of the plotted points of fig. 7 are shown in table 3 below.

[ Table 3]

From (a) to (c) in fig. 7 and table 3, it is understood that: for example, in order to make the resistivity of the n-type contact layer 12 5X 10^-2Omega cm or less, Si concentration is set to 1.2X 10 when growth temperature of n-type contact layer 12 and V/III ratio of raw material gas are 1013 ℃ and 1058, respectively¹⁹～4.0×10¹⁹cm^-3That is, the Si concentration is set to 2.1X 10 when the growth temperature of the n-type contact layer 12 and the V/III ratio of the source gas are 1013 ℃ and 1587, respectively¹⁹～3.2×10¹⁹cm^-3That is, the Si concentration is set to 5.4X 10 when the growth temperature of n-type contact layer 12 and the V/III ratio of the source gas are 1083 ℃ and 1058, respectively¹⁸～2.7×10¹⁹cm^-3And (4) finishing.

Fig. 8 (a) to (c) are graphs showing temperature dependence of the resistivity, carrier concentration, and mobility of n-type contact layer 12. FIGS. 8 (a) to (c) show Si concentrations of 2.10X 10¹⁹cm^-3、3.20×10¹⁹cm^-3、4.30×10¹⁹cm^-3Measured values of these 3 n-type contact layers 12. Si concentration of 2.10X 10¹⁹cm^-3The growth temperature of n-type contact layer 12 and the V/III ratio of the raw material gas were 1013 ℃ C1587, Si concentration of 3.20X 10¹⁹cm^-3The growth temperature of the n-type contact layer 12 and the V/III ratio of the source gas were 1013 ℃ and 1587, respectively, and the Si concentration was 4.30X 10¹⁹cm^-3The growth temperature of the n-type contact layer 12 and the V/III ratio of the source gas are 1043 ℃ and 1587, respectively.

In n-type AlGaN in which the fermi level is degenerate with the conduction band, there is almost no temperature dependence of the carrier concentration. According to (b) in FIG. 8, the Si concentration is 2.10X 10¹⁹cm^-3、3.20×10¹⁹cm^-3、4.30×10¹⁹cm^-3Since the temperature dependence of the carrier concentration is small in any of the n-type contact layers 12 of (1), it can be determined that the fermi level is degenerated with the conduction band.

On the other hand, even when the fermi level and the conduction band are degenerated, if there is a defect of recombination of a group III hole and Si, the carrier is scattered by the defect, and therefore, the mobility depends on the temperature. According to (c) in FIG. 8, the Si concentration is 2.10X 10¹⁹cm^-3、3.20×10¹⁹cm^-3Has almost no temperature dependence of mobility, but has a Si concentration of 4.30X 10¹⁹cm^-3Has a large temperature dependence of mobility in the n-type contact layer 12. This is considered to be because the Si concentration is high and there are a large number of recombination defects of group III holes and Si.

Further, according to (a) in FIG. 8, the Si concentration is 2.10X 10¹⁹cm^-3、3.20×10¹⁹cm^-3Has almost no temperature dependence of resistivity, but has a Si concentration of 4.30X 10¹⁹cm^-3Has a large temperature dependence of resistivity in the n-type contact layer 12.

In the case where the fermi level and the conduction band are not degenerated in AlGaN, the resistivity depends on the temperature, but it can be confirmed from (b) in fig. 8 that the Si concentration is 4.30 × 10¹⁹cm^-3Degeneracy occurs in the n-type contact layer 12, and thus the Si concentration is considered to be 4.30 × 10¹⁹cm^-3The temperature dependence of the resistivity of the n-type contact layer 12 is caused by the presence of a large number of recombination defects of group III holes and Si.

Fig. 9 is a graph showing the relationship between the V/III ratio of the source gas of n-type contact layer 12 and the resistivity. The growth temperature of the n-type contact layer 12 according to fig. 9 is 1013 ℃. Fig. 9 shows that the resistivity becomes minimum when the V/III ratio of the source gas of the n-type contact layer 12 is about 1500, and that a low resistivity is obtained when the V/III ratio of the source gas is in the range of 1000 to 3200. The numerical values of the plotted points of fig. 9 are shown in table 4 below.

[ Table 4]

Fig. 10 is a graph showing the relationship between the growth temperature and the resistivity of the n-type contact layer 12. Fig. 10 shows that the resistance starts to increase during the growth temperature of the n-type contact layer 12 is about 1100 to 1150 ℃. Table 5 below shows the numerical values of the plotted points in fig. 10 and the V/III ratio of the raw material gas of n-type contact layer 12 for each plotted point.

[ Table 5]

Fig. 11 (a) to (c) show spectra (CL spectra) obtained by cathodoluminescence measurement of each n-type contact layer 12. The peak having photon energy around 2.4eV in the CL spectrum of the n-type contact layer 12 is generated by light emission due to a defect of recombination of a group III hole with Si, and the larger the intensity of the peak, the more the defect of recombination of a group III hole with Si.

Note that the peak having a photon energy of about 3.2eV is generated by light emission from C at the group V site, and the peak having a photon energy of about 4.9eV is generated by light emission corresponding to the band gap.

Fig. 11 (a) shows the change in the shape of the CL spectrum of the n-type contact layer 12 according to the Si concentration. From (a) in FIG. 11, the peak due to the recombination defect of the group III hole and Si has a Si concentration of 4.0X 10¹⁸～3.0×10¹⁹cm^-3N-type contact layer of12, it was not confirmed that the concentration of Si was 4.0X 10¹⁹cm^-3A weak peak appears in the n-type contact layer 12 of (2), and the Si concentration is 6.0X 10¹⁹cm^-3A strong peak occurs in the n-type contact layer 12.

Since the more recombination defects of group III holes and Si, the greater the resistance of the n-type contact layer 12, the results obtained from (a) in fig. 11 are consistent with those obtained from (a) to (c) in fig. 7, that is, if the Si concentration of the n-type contact layer 12 exceeds about 4.0 × 10¹⁹cm^-3The resistance increases.

Fig. 11 (b) shows the change in the shape of the CL spectrum of n-type contact layer 12 according to the V/III ratio of the source gas. From fig. 11 (b), no peak due to the recombination defect of the group III hole and Si was observed in the n-type contact layer 12 having the V/III ratio of the source gas of 1100 to 1600, but was observed in the n-type contact layer 12 having the V/III ratio of the source gas of 3200.

Since the resistance of the n-type contact layer 12 increases as the number of recombination defects of group III holes and Si increases, the result obtained from (b) in fig. 11 is consistent with the result obtained from fig. 9, that is, when the V/III ratio of the source gas of the n-type contact layer 12 is in the range of 1000 to 3200, the low resistivity can be obtained.

Fig. 11 (c) shows the change in the shape of the CL spectrum of the n-type contact layer 12 depending on the growth temperature. According to (c) in fig. 11, the peak due to the recombination defect of the group III hole and Si is not observed in the n-type contact layer 12 having the growth temperature of 1010 to 1080 ℃, but is observed in the n-type contact layer 12 having the growth temperature of 1170 ℃.

Since the more the recombination defects of the group III holes and Si, the more the resistance of the n-type contact layer 12 increases, the result obtained from (c) in fig. 11 is consistent with the result obtained from fig. 10, that is, the resistance starts to increase during the growth temperature of the n-type contact layer 12 is about 1100 to 1150 ℃.

Example 2

The evaluation results of the characteristics of the n-type contact layer 212 according to the third embodiment will be described below. In this example, n-type contact layers 212 were formed on a substrate 210 via a buffer layer 211 under various conditions described later, and these n-type contact layers 212 were evaluated. Table 6 below shows the structures and growth conditions of the substrate 210, the buffer layer 211, and the n-type contact layer 212 according to the present example.

[ Table 6]

In this example, the resistivity, carrier concentration, and mobility of the n-type contact layer 212 were measured by hole effect measurement, the Si concentration was measured by Secondary Ion Mass Spectrometry (SIMS), and the transmittance was measured by a spectrophotometer.

FIG. 12 is a graph showing the relationship between the Al component of the n-type contact layer 212 and the transmittance of deep ultraviolet light having a wavelength of 280 nm. The n-type contact layer 212 of fig. 12 has a thickness of 500 nm. Fig. 12 shows: if the Al content of the n-type contact layer 212 is 50% or more, the transmittance of deep ultraviolet light having a wavelength of 280nm exceeds 50%, if the Al content is 55% or more, the transmittance of deep ultraviolet light having a wavelength of 280nm exceeds 70%, and if the Al content is 60% or more, the transmittance of deep ultraviolet light having a wavelength of 280nm becomes almost 100%. This result also applies to the n-type contact layer 216 composed of the same n-type AlGaN as the n-type contact layer 212. The numerical values of the plotted points of fig. 12 are shown in table 7 below.

[ Table 7]

Al composition	Transmittance of light
		0％	0.0％
8％	0.0％
		20％	0.1％
29％	0.2％
		33％	8.3％
40％	21.2％
		63％	100.0％

Fig. 13 is a graph showing the relationship between the Al composition and the resistivity of the n-type contact layer 212. Fig. 13 shows: if the Al composition of the n-type contact layer 212 exceeds about 70%, the resistance increases. This result also applies to the n-type contact layer 216 composed of the same n-type AlGaN as the n-type contact layer 212. The numerical values of the plotted points of fig. 13 are shown in table 8 below.

[ Table 8]

Fig. 14 (a) to (c) are graphs showing the relationship between the Si concentration and the resistivity of n-type contact layer 212. The growth temperature of the n-type contact layer 212 and the V/III ratio of the source gas differ from each other in fig. 14 (a), 14 (b), and 14 (c). Fig. 14 shows that (a) to (c): if the Si concentration of the n-type contact layer 212 exceeds about 4.0 x 10¹⁹

cm

^-3, the resistance increases.

From this result, it can be said that: if the Al content of the n-type contact layer 212 is 50% or more, high transmittance can be ensured for deep ultraviolet light in a wavelength region of 270 to 290nm close to 280nm and light having a wavelength longer than that, and if the Al content is 55% or more, higher transmittance can be ensured, and if the Al content is 60% or more, further higher transmittance can be ensured. This result also applies to the n-type contact layer 216 composed of the same n-type AlGaN as the n-type contact layer 212. The numerical values of the plotted points of fig. 14 are shown in table 9 below.

[ Table 9]

Fig. 15 (a) to (c) are graphs showing temperature dependence of the resistivity, carrier concentration, and mobility of n-type contact layer 212. FIGS. 15 (a) to (c) show Si concentrations of 2.10X 10¹⁹cm^-3、3.20×10¹⁹cm^-3、4.30×10¹⁹cm^-3The measured values of the 3 types of n-type contact layers 212.

In n-type AlGaN in which the fermi level is degenerate with the conduction band, there is almost no temperature dependence of the carrier concentration. According to (b) in FIG. 15, the Si concentration is 2.10X 10¹⁹cm^-3、3.20×10¹⁹cm^-3、4.30×10¹⁹cm^-3Since the temperature dependence of the carrier concentration is small in any of the n-type contact layers 212 of (1), it can be determined that the fermi level is degenerated with the conduction band.

On the other hand, even when the fermi level and the conduction band are degenerated, if there is a defect of recombination of a group III hole and Si, the carrier is scattered by the defect, and therefore, the mobility depends on the temperature. According to (c) in FIG. 15, the Si concentration is 2.10X 10¹⁹cm^-3、3.20×10¹⁹cm^-3Has almost no temperature dependence of mobility, but has a Si concentration of 4.30X 10¹⁹cm^-3Has a large temperature dependence of mobility in the n-type contact layer 212. This is considered to be because since the Si concentration is high, there are a large number of recombination defects of group III holes and Si.

In addition, according to (a) in fig. 15, the Si concentration is 2.10 × 10¹⁹cm^-3、3.20×10¹⁹cm^-3Has almost no temperature dependence of resistivity, but has a Si concentration of 4.30X 10¹⁹cm^-3Has a large temperature dependence of resistivity in the n-type contact layer 212.

In the case where the fermi level and the conduction band are not degenerated in AlGaN, the resistivity depends on the temperature, but it can be confirmed from (b) in fig. 15 that the Si concentration is 4.30 × 10¹⁹cm^-3Is degenerated, so that the Si concentration is considered to be 4.30 × 10¹⁹cm^-3The temperature dependence of the resistivity of the n-type contact layer 212 is due to the presence of a large number of recombination defects of group III holes with Si.

Fig. 16 shows spectra (CL spectra) obtained by cathodoluminescence measurement of each n-type contact layer 212. The peak having photon energy around 2.4eV in the CL spectrum of the n-type contact layer 212 is generated by light emission due to a defect in which a group III hole and Si are combined, and the greater the intensity of the peak, the more defects in which a group III hole and Si are combined.

Fig. 16 shows the shape of the CL spectrum of the n-type contact layer 212 as a function of the Si concentration. From FIG. 16, the peak due to the recombination defect of the group III hole and Si was 4.0X 10 in the Si concentration¹⁸～3.0×10¹⁹cm^-3Is not observed in the n-type contact layer 212 (2), the Si concentration is 4.0X 10¹⁹cm^-3A weak peak appears in the n-type contact layer 212 of (2), and the Si concentration is 6.0 × 10¹⁹cm^-3A strong peak occurs in the n-type contact layer 212.

Since the more recombination defects of group III holes and Si, the greater the resistance of the n-type contact layer 212, the results obtained from fig. 16 are consistent with the results obtained from (a) to (c) of fig. 14, that is, if the Si concentration of the n-type contact layer 212 exceeds about 4.0 × 10¹⁹cm^-3The resistance increases.

The embodiments and examples of the present invention have been described above, but the present invention is not limited to the embodiments and examples described above, and various modifications can be made without departing from the spirit of the present invention. In addition, the components of the above embodiments and examples may be arbitrarily combined without departing from the scope of the invention.

The embodiments and examples described above do not limit the invention according to the scope of claims. In addition, it should be noted that not all combinations of the features described in the embodiments and examples are essential in means for solving the problems of the invention.

Claims

1. A light-emitting element is provided with:

an n-type contact layer of AlGaN whose Fermi level is degenerate with the conduction band, and

a light-emitting layer composed of AlGaN and laminated on the n-type contact layer;

the Al composition of the n-type contact layer is 10% or more and 70% or less greater than the Al composition of the light-emitting layer,

the n-type contact layer is at a concentration at which the degeneracy occurs and is 4.0 x 10¹⁹cm^-3The following concentrations contain Si.

2. The light-emitting element according to claim 1, wherein an Al component of the n-type contact layer is 50% or more.

3. The light-emitting element according to claim 1 or 2, wherein a concentration of Si contained in the n-type contact layer is 1.6 x 10¹⁸cm^-3The above.

4. The light-emitting element according to any one of claims 1 to 3, wherein the n-type contact layer has a resistivity of 5 x 10^-2Omega cm or less.

5. A method for manufacturing a light-emitting element includes the steps of:

a step of forming an n-type contact layer made of AlGaN in which the Fermi level is degenerate with the conduction band by vapor deposition, and

forming a light-emitting layer made of AlGaN on the n-type contact layer;

the Al component of the n-type contact layer is larger than that of the light-emitting layer by 10% or more and 70% or less,

the n-type contact layer is at a concentration at which the degeneracy occurs and is 4.0 x 10¹⁹cm^-3The following concentrations contain Si in a form of Si,

the V/III ratio of the raw material gas of the n-type contact layer in the step of forming the n-type contact layer is within the range of 1000 to 3200.

6. The method for manufacturing a light-emitting element according to claim 5, wherein a growth temperature of the n-type contact layer in the step of forming the n-type contact layer is 1150 ℃ or lower.

7. A light-emitting element is provided with:

an n-type contact layer made of n-type AlGaN,

a light emitting layer emitting deep ultraviolet light on the n-type contact layer,

a current diffusion layer composed of AlGaN containing two-dimensional hole gas on the light emitting layer,

a p-type contact layer connected to a part of the upper surface of the current diffusion layer and composed of p-type GaN or p-type AlGaN having an Al component of 35% or less,

an n-electrode connected to the n-type contact layer, and

and the p electrode is connected with the p-type contact layer.

8. The light-emitting element according to claim 7, wherein the current diffusion layer has: a first AlGaN layer composed of p-type AlGaN having an Al component in a range of 50% to 70%, and a second AlGaN layer directly provided on the first AlGaN layer and composed of p-type or i-type AlGaN having an Al component in a range of 30% to 50%;

9. The light-emitting element according to claim 7 or 8, wherein an area of a region of the upper surface of the current diffusion layer, which contacts the p-type contact layer, is in a range of 40% to 80% of an area of an entire region of the upper surface.

10. The light-emitting element according to any one of claims 7 to 9, wherein at least a part of a region of the upper surface of the current diffusion layer other than a region to which the p-type contact layer is connected is covered with a passivation film made of an insulating material.

11. The light-emitting element according to any one of claims 7 to 10, wherein a light-reflecting layer is provided over a region other than a region where the p-type contact layer is connected to the upper surface of the current diffusion layer.

12. A light-emitting element is provided with:

a first n-type contact layer composed of AlGaN,

a light emitting layer emitting deep ultraviolet light on the first n-type contact layer,

a p-type layer composed of AlGaN on the light emitting layer,

a second n-type contact layer composed of AlGaN and forming a tunnel junction with the p-type layer, the second n-type contact layer being degenerate in a Fermi level and a conduction band,

an n-electrode connected to the first n-type contact layer, and

a p-electrode connected to the second n-type contact layer;

the Al component of the second n-type contact layer is in the range of 40-70%.

13. The light-emitting element according to claim 12, wherein the p-type layer contains a two-dimensional hole gas.

14. The light-emitting element according to claim 12 or 13, wherein the n-type contact layer is formed so as to cause the reductionAnd the concentration of the alpha-olefin is 4.0X 10¹⁹cm^-3The following concentrations contain Si.

15. The light-emitting element according to any one of claims 12 to 14, wherein a portion of the n-electrode which is in contact with the first n-type contact layer and a portion of the p-electrode which is in contact with the second n-type contact layer are composed of the same material.

16. The light-emitting element according to claim 15, wherein the material is aluminum.